Evaluation of the Safety of Emicizumab Prophylaxis in Persons with Hemophilia A: An Updated Summary of Thrombotic Events and Thrombotic Microangiopathies

Background: Emicizumab is indicated for routine prophylaxis in persons with congenital hemophilia A (PwcHA) with/without factor (F)VIII inhibitors in >100 and >80 countries, respectively. Emicizumab has been used by >11,400 persons across the globe (data cut-off 15 May 2021). The pivotal HAVEN 1-4 trials established the efficacy and safety of emicizumab prophylaxis; however, the HAVEN 1 trial identified an increased risk of thrombotic events (TEs) and thrombotic microangiopathies (TMAs) when used in conjunction with >100 U/kg/24 hours activated prothrombin complex concentrate (aPCC) for ≥24 hours (Oldenburg, et al. New Engl J Med 2017). Here we report an updated safety evaluation of emicizumab prophylaxis focusing on TEs and TMAs.

Methods: All individual safety reports for emicizumab from clinical trials, registries, expanded access programs, compassionate use and the post-marketing setting were collated with a cut-off date of 15 May 2021 and analyzed for TEs and TMAs. Number of TEs/TMAs, clinical factors (indication, age, FVIII inhibitor status, comorbidities) and drug factors (co-exposure to medications affecting coagulation) are presented in aggregate. Individual case reports (cases) were reviewed to exclude non-TEs and any duplicate reports. TEs were identified using the Medical Dictionary for Regulatory Activities (MedDRA) search strategy: 'Embolic and Thrombotic Events' Standardized Medical Query ([SMQ] Wide) and Preferred Term 'Acute Coronary Syndrome'. TMAs were defined as hemolytic uremic syndrome, microangiopathic hemolytic anemia, microangiopathy, thrombotic microangiopathy and thrombotic thrombocytopenic purpura.

Results: In total, 52 cases (56 events) meeting the search criteria were identified on the Roche Global Safety Database as of 15 May 2021 (Figure). After review, 39 cases were reported in PwcHA and 10 cases were determined to be off-label (acquired hemophilia A, n=7; or unknown indication, n=3). Two additional cases were determined to be duplicates. One case of 'hemiparesis' was identified through SMQ review, but did not fit the clinical definition of a true TE. Six cases occurred with concomitant aPCC use, of which four were TMAs. In total, 33 cases were not associated with concomitant aPCC use, and these comprised 37 TEs and no TMAs in PwcHA. No new TEs or TMAs associated with aPCC were reported since the last update (Lee, et al. Haemophilia 2020).

For the 37 TEs reported in PwcHA and not associated with aPCC, the median age (range) at time of event was 49 years (0.42-84) and the median (range) emicizumab treatment duration at time of event was 330 days (0-1076). In total, 36 (97.3%) TEs were medically confirmed and one (2.7%) was patient reported. Seventeen (45.9%) TEs occurred in PwcHA with FVIII inhibitors. Seven (18.9%) TEs were associated with central venous access devices (CVADs), of which four were reported to be resolving/recovering at last report. All except for two (with limited information) non-aPCC associated TEs in PwcHA were associated with ≥1 cardiovascular (CV) risk factors (e.g. previous myocardial infarction, ischemic heart disease, coronary artery disease, hypertension, hyperlipidemia, smoking, advanced age) or other risk factors for thrombosis (e.g. sepsis/bacteremia, device use, coinciding injury, hepatitis C).

Of the non-aPCC and non-CVAD associated events reported, six (20.0%) TEs led to the discontinuation of emicizumab. Across all non-aPCC associated events, an evaluation of latency or duration of treatment did not reveal any patterns or trends. In total, four TEs were fatal: two myocardial infarctions, both in medically complex patients; and two disseminated intravascular coagulation events in patients >70 years of age with pneumonia. Where reported, 20/31 (64.5%) TEs were recovered/resolving at the time of this analysis, with the majority of these cases reporting no change to emicizumab prophylaxis as a result of the event.

Conclusions: The reporting rate for TEs without concomitant aPCC remains low as exposure increases. Notably, all cases with adequate information available were associated with CV risk factors and/or risk factors for thrombosis. All TMAs were associated with concomitant use of aPCC. This post-marketing analysis does not support TEs and TMAs without concomitant aPCC as an identified risk for PwcHA receiving emicizumab prophylaxis. The risk-benefit profile of emicizumab remains unchanged.

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